import json
from collections import Counter

from django.apps import apps
from django.contrib.admin.models import ADDITION, CHANGE, DELETION, LogEntry
from django.utils import timezone

from .models import AuditEvent
from .resolvers import (
    allocation_label,
    allocation_label_from_parts,
    project_label,
    project_label_from_id,
    project_user_label,
    user_label,
    user_profile_label_from_id,
)
from .utils import ACTION_EVIDENCE_MAP


RUN_NAME = "initial_historical_backfill"
ADMIN_SOURCE = AuditEvent.Source.DJANGO_ADMIN_LOG
HISTORY_SOURCE = AuditEvent.Source.COLDFRONT_HISTORY


class BackfillReport:
    def __init__(self):
        self.examined = Counter()
        self.created = Counter()
        self.would_create = Counter()
        self.duplicates = 0
        self.ambiguous = 0
        self.by_action = Counter()
        self.by_evidence = Counter()

    def record_examined(self, source):
        self.examined[source] += 1

    def record_duplicate(self):
        self.duplicates += 1

    def record_ambiguous(self):
        self.ambiguous += 1

    def record_event(self, action, evidence_category, dry_run):
        if dry_run:
            self.would_create[action] += 1
        else:
            self.created[action] += 1
        self.by_action[action] += 1
        self.by_evidence[evidence_category or "unclassified"] += 1

    @property
    def created_events(self):
        return sum(self.created.values())

    @property
    def would_create_events(self):
        return sum(self.would_create.values())


def _json_message(change_message):
    if not change_message:
        return ""
    if isinstance(change_message, str):
        return change_message
    return json.dumps(change_message, default=str)


def _changed_fields(change_message):
    if not change_message:
        return []
    try:
        entries = json.loads(change_message) if isinstance(change_message, str) else change_message
    except (TypeError, ValueError):
        return []
    fields = []
    for entry in entries:
        changed = entry.get("changed", {}) if isinstance(entry, dict) else {}
        fields.extend(changed.get("fields", []))
    return fields


def _has_changed_field(change_message, field_name):
    normalized = {field.lower().replace("_", " ") for field in _changed_fields(change_message)}
    return field_name.lower().replace("_", " ") in normalized


def _target_from_logentry(log_entry):
    if not log_entry.content_type_id:
        return "", "", log_entry.object_id or "", log_entry.object_repr
    app_label = log_entry.content_type.app_label
    model_name = log_entry.content_type.model
    return app_label, model_name, log_entry.object_id or "", log_entry.object_repr


def _defaults_for_action(action):
    evidence_category, control_family = ACTION_EVIDENCE_MAP.get(action, ("", ""))
    return evidence_category, control_family


def _create_event(
    *,
    action,
    source,
    source_id,
    event_time,
    actor,
    target_type,
    target_id,
    target_repr,
    message,
    old_values=None,
    new_values=None,
    dry_run,
    report,
):
    if AuditEvent.objects.filter(source=source, source_id=str(source_id), action=action).exists():
        report.record_duplicate()
        return None

    evidence_category, control_family = _defaults_for_action(action)
    report.record_event(action, evidence_category, dry_run)
    if dry_run:
        return None

    return AuditEvent.objects.create(
        actor=actor,
        action=action,
        evidence_category=evidence_category,
        control_family=control_family,
        target_type=target_type,
        target_id=str(target_id or "")[:128],
        target_repr=str(target_repr or "")[:255],
        old_values=old_values or {},
        new_values=new_values or {},
        message=message,
        source=source,
        source_id=str(source_id)[:128],
        is_reconstructed=True,
        event_time=event_time,
    )


def _admin_action(log_entry):
    if log_entry.action_flag == ADDITION:
        return AuditEvent.Action.ADMIN_ADDITION
    if log_entry.action_flag == CHANGE:
        return AuditEvent.Action.ADMIN_CHANGE
    if log_entry.action_flag == DELETION:
        return AuditEvent.Action.ADMIN_DELETION
    return None


def _admin_message(log_entry, action, object_repr=None):
    change_message = _json_message(log_entry.change_message)
    target_repr = object_repr or log_entry.object_repr
    if action == AuditEvent.Action.ADMIN_ADDITION:
        verb = "added"
    elif action == AuditEvent.Action.ADMIN_DELETION:
        verb = "deleted"
    else:
        verb = "changed"
    suffix = f" Change message: {change_message}" if change_message else ""
    return f"Reconstructed from Django admin log: admin {verb} {target_repr}.{suffix}"


def _admin_target_repr(log_entry, target_type, object_id, object_repr):
    if target_type == "user.userprofile":
        return user_profile_label_from_id(object_id)
    if target_type == "project.project" and log_entry.action_flag == DELETION:
        return f"Deleted project: {object_repr} (id {object_id})"
    return object_repr


def backfill_admin_log(*, dry_run, report):
    for log_entry in LogEntry.objects.select_related("content_type", "user").order_by("pk"):
        report.record_examined("django_admin_log")
        action = _admin_action(log_entry)
        if action is None:
            report.record_ambiguous()
            continue

        app_label, model_name, object_id, object_repr = _target_from_logentry(log_entry)
        target_type = f"{app_label}.{model_name}" if app_label and model_name else ""
        target_repr = _admin_target_repr(log_entry, target_type, object_id, object_repr)
        change_message = _json_message(log_entry.change_message)
        _create_event(
            action=action,
            source=ADMIN_SOURCE,
            source_id=log_entry.pk,
            event_time=log_entry.action_time,
            actor=log_entry.user,
            target_type=target_type,
            target_id=object_id,
            target_repr=target_repr,
            message=_admin_message(log_entry, action, target_repr),
            new_values={"change_message": change_message, "content_type": target_type},
            dry_run=dry_run,
            report=report,
        )

        for semantic in _semantic_events_from_logentry(log_entry, target_type, object_id, target_repr, change_message):
            _create_event(
                source=ADMIN_SOURCE,
                source_id=log_entry.pk,
                event_time=log_entry.action_time,
                actor=log_entry.user,
                dry_run=dry_run,
                report=report,
                **semantic,
            )


def _semantic_events_from_logentry(log_entry, target_type, object_id, object_repr, change_message):
    events = []
    prefix = "Reconstructed from Django admin log:"
    fields = ", ".join(_changed_fields(change_message)) or "unknown fields"

    if target_type == "user.userprofile" and _has_changed_field(change_message, "Is pi"):
        events.append(
            {
                "action": AuditEvent.Action.USER_PI_UPGRADED,
                "target_type": target_type,
                "target_id": object_id,
                "target_repr": object_repr,
                "message": f"{prefix} PI status changed for {object_repr}; direction unknown",
                "new_values": {"change_message": change_message, "direction": "unknown"},
            }
        )
    elif target_type == "project.projectuser" and _has_changed_field(change_message, "Role"):
        events.append(
            {
                "action": AuditEvent.Action.PROJECT_USER_ROLE_CHANGED,
                "target_type": target_type,
                "target_id": object_id,
                "target_repr": object_repr,
                "message": f"{prefix} project user role changed for {object_repr}; exact old/new roles unknown.",
                "new_values": {"change_message": change_message, "fields": fields},
            }
        )
    elif target_type == "resource.resource":
        resource_action = {
            ADDITION: AuditEvent.Action.RESOURCE_CREATED,
            CHANGE: AuditEvent.Action.RESOURCE_CHANGED,
            DELETION: AuditEvent.Action.RESOURCE_DELETED,
        }.get(log_entry.action_flag)
        if resource_action:
            events.append(
                {
                    "action": resource_action,
                    "target_type": target_type,
                    "target_id": object_id,
                    "target_repr": object_repr,
                    "message": f"{prefix} resource event for {object_repr}.",
                    "new_values": {"change_message": change_message, "fields": fields},
                }
            )
    elif target_type == "project.project":
        project_action = {
            ADDITION: AuditEvent.Action.PROJECT_CREATED,
            DELETION: AuditEvent.Action.PROJECT_DELETED,
        }.get(log_entry.action_flag)
        if project_action:
            events.append(
                {
                    "action": project_action,
                    "target_type": target_type,
                    "target_id": object_id,
                    "target_repr": object_repr,
                    "message": f"{prefix} project event for {object_repr}.",
                    "new_values": {"change_message": change_message, "fields": fields},
                }
            )
        elif log_entry.action_flag == CHANGE and _has_changed_field(change_message, "Pi"):
            events.append(
                {
                    "action": AuditEvent.Action.PROJECT_PI_CHANGED,
                    "target_type": target_type,
                    "target_id": object_id,
                    "target_repr": object_repr,
                    "message": f"{prefix} project PI changed for {object_repr}; exact old/new PI unknown.",
                    "new_values": {"change_message": change_message, "fields": fields},
                }
            )
        elif log_entry.action_flag == CHANGE and _has_changed_field(change_message, "Status"):
            events.append(
                {
                    "action": AuditEvent.Action.PROJECT_STATUS_CHANGED,
                    "target_type": target_type,
                    "target_id": object_id,
                    "target_repr": object_repr,
                    "message": f"{prefix} project status changed for {object_repr}; exact old/new status unknown.",
                    "new_values": {"change_message": change_message, "fields": fields},
                }
            )
    return events


def _model_or_none(label):
    try:
        return apps.get_model(label)
    except LookupError:
        return None


def _choice_name(model_label, pk):
    if pk in (None, ""):
        return None
    model = _model_or_none(model_label)
    if model is None:
        return str(pk)
    try:
        return model.objects.get(pk=pk).name
    except Exception:
        return str(pk)


def _history_source_id(model_label, history):
    return f"{model_label}:{history.history_id}"


def _history_actor(history):
    return getattr(history, "history_user", None)


def _resource_repr(history):
    if getattr(history, "name", ""):
        return f"Resource: {history.name}"
    return f"Resource id {history.id}"


def _project_reference(project_id):
    if project_id in (None, ""):
        return "Project unknown"
    Project = _model_or_none("project.Project")
    if Project is None:
        return f"Project id {project_id} (model unavailable)"
    return project_label_from_id(project_id)


def _project_history_repr(history, *, deleted=False):
    title = getattr(history, "title", "") or f"Project id {history.id}"
    if deleted:
        return f"Deleted project: {title} (id {history.id})"
    current_label = project_label_from_id(history.id)
    if "(not found)" not in current_label:
        return current_label
    return f"Project: {title} (id {history.id})"


def _user_reference(user_id):
    if user_id in (None, ""):
        return "User unknown"
    User = _model_or_none("auth.User")
    if User is None:
        return f"User id {user_id} (model unavailable)"
    try:
        return f"{user_label(User.objects.get(pk=user_id))} (id {user_id})"
    except Exception:
        return f"User id {user_id} (not found)"


def _allocation_repr(history):
    Allocation = _model_or_none("allocation.Allocation")
    if Allocation is not None:
        try:
            return allocation_label(Allocation.objects.get(pk=history.id))
        except Exception:
            pass
    resource_names = getattr(history, "resource_names", [])
    return allocation_label_from_parts(resource_names, _project_reference(getattr(history, "project_id", None)))


def _project_user_repr(history):
    ProjectUser = _model_or_none("project.ProjectUser")
    if ProjectUser is not None:
        try:
            return project_user_label(ProjectUser.objects.get(pk=history.id))
        except Exception:
            pass
    return (
        f"Project user {history.id}: "
        f"{_user_reference(getattr(history, 'user_id', None))} on "
        f"{_project_reference(getattr(history, 'project_id', None))}"
    )


def _iter_adjacent(history_model):
    rows = list(history_model.objects.order_by("id", "history_date", "history_id"))
    previous_by_id = {}
    for row in rows:
        previous = previous_by_id.get(row.id)
        yield previous, row
        previous_by_id[row.id] = row


def backfill_history(*, dry_run, report):
    _backfill_project_history(dry_run=dry_run, report=report)
    _backfill_resource_history(dry_run=dry_run, report=report)
    _backfill_project_user_history(dry_run=dry_run, report=report)
    _backfill_allocation_history(dry_run=dry_run, report=report)


def _backfill_project_history(*, dry_run, report):
    model_label = "project.HistoricalProject"
    model = _model_or_none(model_label)
    if model is None:
        return
    for previous, history in _iter_adjacent(model):
        report.record_examined(model_label)
        if history.history_type == "+":
            _create_event(
                action=AuditEvent.Action.PROJECT_CREATED,
                source=HISTORY_SOURCE,
                source_id=_history_source_id(model_label, history),
                event_time=history.history_date,
                actor=_history_actor(history),
                target_type="project.project",
                target_id=history.id,
                target_repr=_project_history_repr(history),
                message=f"Reconstructed from ColdFront history: project created: {_project_history_repr(history)}.",
                new_values=_project_history_values(history),
                dry_run=dry_run,
                report=report,
            )
            continue

        if history.history_type == "-":
            _create_event(
                action=AuditEvent.Action.PROJECT_DELETED,
                source=HISTORY_SOURCE,
                source_id=_history_source_id(model_label, history),
                event_time=history.history_date,
                actor=_history_actor(history),
                target_type="project.project",
                target_id=history.id,
                target_repr=_project_history_repr(history, deleted=True),
                message=f"Reconstructed from ColdFront history: project deleted: {_project_history_repr(history, deleted=True)}.",
                old_values=_project_history_values(history),
                dry_run=dry_run,
                report=report,
            )
            continue

        if history.history_type != "~" or previous is None:
            report.record_ambiguous()
            continue

        event_created = False
        if previous.status_id != history.status_id:
            old_status = _choice_name("project.ProjectStatusChoice", previous.status_id)
            new_status = _choice_name("project.ProjectStatusChoice", history.status_id)
            action = (
                AuditEvent.Action.PROJECT_ARCHIVED
                if new_status == "Archived"
                else AuditEvent.Action.PROJECT_STATUS_CHANGED
            )
            _create_event(
                action=action,
                source=HISTORY_SOURCE,
                source_id=_history_source_id(model_label, history),
                event_time=history.history_date,
                actor=_history_actor(history),
                target_type="project.project",
                target_id=history.id,
                target_repr=_project_history_repr(history),
                message=f"Reconstructed from ColdFront history: project status changed from {old_status} to {new_status}.",
                old_values={"status": old_status, "pi_id": previous.pi_id},
                new_values={"status": new_status, "pi_id": history.pi_id},
                dry_run=dry_run,
                report=report,
            )
            event_created = True

        if previous.pi_id != history.pi_id:
            _create_event(
                action=AuditEvent.Action.PROJECT_PI_CHANGED,
                source=HISTORY_SOURCE,
                source_id=_history_source_id(model_label, history),
                event_time=history.history_date,
                actor=_history_actor(history),
                target_type="project.project",
                target_id=history.id,
                target_repr=_project_history_repr(history),
                message=(
                    "Reconstructed from ColdFront history: project PI changed "
                    f"from {_user_reference(previous.pi_id)} to {_user_reference(history.pi_id)}."
                ),
                old_values={"pi_id": previous.pi_id},
                new_values={"pi_id": history.pi_id},
                dry_run=dry_run,
                report=report,
            )
            event_created = True

        if not event_created:
            report.record_ambiguous()


def _backfill_resource_history(*, dry_run, report):
    model_label = "resource.HistoricalResource"
    model = _model_or_none(model_label)
    if model is None:
        return
    tracked = ("name", "description", "is_available", "is_public", "is_allocatable", "requires_payment")
    for previous, history in _iter_adjacent(model):
        report.record_examined(model_label)
        if history.history_type == "+":
            action = AuditEvent.Action.RESOURCE_CREATED
        elif history.history_type == "-":
            action = AuditEvent.Action.RESOURCE_DELETED
        elif history.history_type == "~" and previous is not None and any(
            getattr(previous, field) != getattr(history, field) for field in tracked
        ):
            action = AuditEvent.Action.RESOURCE_CHANGED
        else:
            report.record_ambiguous()
            continue
        _create_event(
            action=action,
            source=HISTORY_SOURCE,
            source_id=_history_source_id(model_label, history),
            event_time=history.history_date,
            actor=_history_actor(history),
            target_type="resource.resource",
            target_id=history.id,
            target_repr=_resource_repr(history),
            message=f"Reconstructed from ColdFront history: resource {_resource_repr(history)} {action.label.lower()}.",
            old_values=_history_values(previous, tracked) if previous else {},
            new_values=_history_values(history, tracked) if history.history_type != "-" else {},
            dry_run=dry_run,
            report=report,
        )


def _backfill_project_user_history(*, dry_run, report):
    model_label = "project.HistoricalProjectUser"
    model = _model_or_none(model_label)
    if model is None:
        return
    for previous, history in _iter_adjacent(model):
        report.record_examined(model_label)
        if history.history_type != "~" or previous is None or previous.role_id == history.role_id:
            report.record_ambiguous()
            continue
        old_role = _choice_name("project.ProjectUserRoleChoice", previous.role_id)
        new_role = _choice_name("project.ProjectUserRoleChoice", history.role_id)
        _create_event(
            action=AuditEvent.Action.PROJECT_USER_ROLE_CHANGED,
            source=HISTORY_SOURCE,
            source_id=_history_source_id(model_label, history),
            event_time=history.history_date,
            actor=_history_actor(history),
            target_type="project.projectuser",
            target_id=history.id,
            target_repr=_project_user_repr(history),
            message=f"Reconstructed from ColdFront history: project user role changed from {old_role} to {new_role}.",
            old_values={"role": old_role, "project_id": previous.project_id, "user_id": previous.user_id},
            new_values={"role": new_role, "project_id": history.project_id, "user_id": history.user_id},
            dry_run=dry_run,
            report=report,
        )


def _backfill_allocation_history(*, dry_run, report):
    model_label = "allocation.HistoricalAllocation"
    model = _model_or_none(model_label)
    if model is None:
        return
    for previous, history in _iter_adjacent(model):
        report.record_examined(model_label)
        if history.history_type != "~" or previous is None:
            report.record_ambiguous()
            continue

        if previous.status_id != history.status_id:
            new_status = _choice_name("allocation.AllocationStatusChoice", history.status_id)
            old_status = _choice_name("allocation.AllocationStatusChoice", previous.status_id)
            action = AuditEvent.Action.ALLOCATION_DISABLED if new_status in {"Denied", "Revoked", "Disabled"} else AuditEvent.Action.ALLOCATION_STATUS_CHANGED
            _create_event(
                action=action,
                source=HISTORY_SOURCE,
                source_id=_history_source_id(model_label, history),
                event_time=history.history_date,
                actor=_history_actor(history),
                target_type="allocation.allocation",
                target_id=history.id,
                target_repr=_allocation_repr(history),
                message=f"Reconstructed from ColdFront history: allocation status changed from {old_status} to {new_status}.",
                old_values={"status": old_status, "project_id": previous.project_id},
                new_values={"status": new_status, "project_id": history.project_id},
                dry_run=dry_run,
                report=report,
            )

        if previous.end_date and history.end_date and history.end_date > previous.end_date:
            _create_event(
                action=AuditEvent.Action.ALLOCATION_RENEWED,
                source=HISTORY_SOURCE,
                source_id=_history_source_id(model_label, history),
                event_time=history.history_date,
                actor=_history_actor(history),
                target_type="allocation.allocation",
                target_id=history.id,
                target_repr=_allocation_repr(history),
                message=f"Reconstructed from ColdFront history: allocation end date increased from {previous.end_date} to {history.end_date}.",
                old_values={"end_date": previous.end_date.isoformat(), "project_id": previous.project_id},
                new_values={"end_date": history.end_date.isoformat(), "project_id": history.project_id},
                dry_run=dry_run,
                report=report,
            )


def _history_values(history, fields):
    if history is None:
        return {}
    return {field: getattr(history, field) for field in fields}


def _project_history_values(history):
    return {
        "title": history.title,
        "status": _choice_name("project.ProjectStatusChoice", history.status_id),
        "status_id": history.status_id,
        "pi_id": history.pi_id,
        "project_code": history.project_code,
    }


def run_backfill(*, dry_run):
    report = BackfillReport()
    backfill_admin_log(dry_run=dry_run, report=report)
    backfill_history(dry_run=dry_run, report=report)
    return report