#!/usr/bin/env bash
#
# Auto-Merge PR Script
#
# Automatically merges a PR to develop if all quality gates pass.
# This script can be called from Woodpecker CI or manually.
#
# Usage:
#   auto-merge-pr.sh <pr_number>
#
# Environment variables:
#   GITEA_TOKEN - Gitea API token (required)
#   GITEA_URL - Gitea instance URL (default: https://git.mosaicstack.dev)
#   REPO_OWNER - Repository owner (default: mosaic)
#   REPO_NAME - Repository name (default: stack)
#   TARGET_BRANCH - Target branch for auto-merge (default: develop)
#   DRY_RUN - If set, only check eligibility without merging (default: false)

set -euo pipefail

# Configuration
GITEA_URL="${GITEA_URL:-https://git.mosaicstack.dev}"
REPO_OWNER="${REPO_OWNER:-mosaic}"
REPO_NAME="${REPO_NAME:-stack}"
TARGET_BRANCH="${TARGET_BRANCH:-develop}"
DRY_RUN="${DRY_RUN:-false}"

# Colors for output
RED='\033[0;31m'
GREEN='\033[0;32m'
YELLOW='\033[1;33m'
BLUE='\033[0;34m'
NC='\033[0m' # No Color

# Functions
log_info() {
    echo -e "${BLUE}ℹ️  $1${NC}"
}

log_success() {
    echo -e "${GREEN}✅ $1${NC}"
}

log_warning() {
    echo -e "${YELLOW}⚠️  $1${NC}"
}

log_error() {
    echo -e "${RED}❌ $1${NC}"
}

# Check requirements
if [ -z "${GITEA_TOKEN:-}" ]; then
    log_error "GITEA_TOKEN environment variable is required"
    exit 1
fi

if [ $# -lt 1 ]; then
    log_error "Usage: $0 <pr_number>"
    exit 1
fi

PR_NUMBER="$1"
API_BASE="$GITEA_URL/api/v1/repos/$REPO_OWNER/$REPO_NAME"

log_info "Checking PR #$PR_NUMBER for auto-merge eligibility..."

# Fetch PR details
PR_DATA=$(curl -sf -H "Authorization: token $GITEA_TOKEN" \
    "$API_BASE/pulls/$PR_NUMBER" || {
    log_error "Failed to fetch PR #$PR_NUMBER"
    exit 1
})

# Extract PR information
PR_STATE=$(echo "$PR_DATA" | jq -r '.state // ""')
PR_MERGED=$(echo "$PR_DATA" | jq -r '.merged // false')
BASE_BRANCH=$(echo "$PR_DATA" | jq -r '.base.ref // ""')
HEAD_BRANCH=$(echo "$PR_DATA" | jq -r '.head.ref // ""')
IS_MERGEABLE=$(echo "$PR_DATA" | jq -r '.mergeable // false')
HAS_CONFLICTS=$(echo "$PR_DATA" | jq -r '.mergeable_state // "unknown"')
PR_TITLE=$(echo "$PR_DATA" | jq -r '.title // "Unknown"')

log_info "PR #$PR_NUMBER: $PR_TITLE"
log_info "  State: $PR_STATE"
log_info "  Base: $BASE_BRANCH ← Head: $HEAD_BRANCH"
log_info "  Mergeable: $IS_MERGEABLE ($HAS_CONFLICTS)"

# Check if PR is already merged
if [ "$PR_MERGED" = "true" ]; then
    log_success "PR is already merged"
    exit 0
fi

# Check if PR is open
if [ "$PR_STATE" != "open" ]; then
    log_warning "PR is not open (state: $PR_STATE)"
    exit 0
fi

# Check if PR targets the correct branch
if [ "$BASE_BRANCH" != "$TARGET_BRANCH" ]; then
    log_warning "PR does not target $TARGET_BRANCH (targets: $BASE_BRANCH)"
    exit 0
fi

# Check if PR is mergeable
if [ "$IS_MERGEABLE" != "true" ]; then
    log_error "PR is not mergeable (state: $HAS_CONFLICTS)"
    exit 1
fi

# Fetch CI status checks
log_info "Checking CI status..."
STATUS_DATA=$(curl -sf -H "Authorization: token $GITEA_TOKEN" \
    "$API_BASE/statuses/$(echo "$PR_DATA" | jq -r '.head.sha')" || echo "[]")

# Count status check results
TOTAL_CHECKS=$(echo "$STATUS_DATA" | jq 'length')
SUCCESS_CHECKS=$(echo "$STATUS_DATA" | jq '[.[] | select(.state == "success")] | length')
PENDING_CHECKS=$(echo "$STATUS_DATA" | jq '[.[] | select(.state == "pending")] | length')
FAILURE_CHECKS=$(echo "$STATUS_DATA" | jq '[.[] | select(.state == "failure" or .state == "error")] | length')

log_info "  Total checks: $TOTAL_CHECKS"
log_info "  Success: $SUCCESS_CHECKS"
log_info "  Pending: $PENDING_CHECKS"
log_info "  Failed: $FAILURE_CHECKS"

# Check if there are any failures
if [ "$FAILURE_CHECKS" -gt 0 ]; then
    log_error "PR has $FAILURE_CHECKS failed status checks"
    echo "$STATUS_DATA" | jq -r '.[] | select(.state == "failure" or .state == "error") | "  - \(.context): \(.description)"'
    exit 1
fi

# Check if there are pending checks
if [ "$PENDING_CHECKS" -gt 0 ]; then
    log_warning "PR has $PENDING_CHECKS pending status checks - waiting..."
    exit 0
fi

# Check if all required checks passed
if [ "$TOTAL_CHECKS" -eq 0 ]; then
    log_warning "No status checks found - proceeding with caution"
elif [ "$SUCCESS_CHECKS" -ne "$TOTAL_CHECKS" ]; then
    log_warning "Not all status checks are successful ($SUCCESS_CHECKS/$TOTAL_CHECKS)"
fi

# All checks passed - ready to merge
log_success "All quality gates passed!"

if [ "$DRY_RUN" = "true" ]; then
    log_info "DRY RUN: Would merge PR #$PR_NUMBER to $TARGET_BRANCH"
    exit 0
fi

# Perform the merge
log_info "Merging PR #$PR_NUMBER to $TARGET_BRANCH..."
MERGE_RESULT=$(curl -sf -X POST \
    -H "Authorization: token $GITEA_TOKEN" \
    -H "Content-Type: application/json" \
    -d '{
        "Do": "merge",
        "MergeMessageField": "",
        "MergeTitleField": "",
        "delete_branch_after_merge": true,
        "force_merge": false,
        "merge_when_checks_succeed": false
    }' \
    "$API_BASE/pulls/$PR_NUMBER/merge" || {
    log_error "Failed to merge PR #$PR_NUMBER"
    exit 1
})

# Check if merge was successful
if echo "$MERGE_RESULT" | jq -e '.merged' > /dev/null 2>&1; then
    MERGE_SHA=$(echo "$MERGE_RESULT" | jq -r '.sha // "unknown"')
    log_success "Successfully merged PR #$PR_NUMBER to $TARGET_BRANCH"
    log_success "  Merge commit: $MERGE_SHA"
    log_success "  Branch $HEAD_BRANCH deleted"
else
    ERROR_MSG=$(echo "$MERGE_RESULT" | jq -r '.message // "Unknown error"')
    log_error "Merge failed: $ERROR_MSG"
    exit 1
fi