package mountain_pass

import (
	"context"
	"database/sql"
	"fmt"
	"io"
	"log/slog"
	"os"
	"strconv"
	"strings"

	"github.com/paulmach/osm"
	"github.com/paulmach/osm/osmpbf"
)

const insertStatement = `
	INSERT INTO mountain_passes (osm_id, name, elevation, latitude, longitude, category)
	VALUES (?, ?, ?, ?, ?, ?)
	ON CONFLICT(osm_id) DO UPDATE SET
		name = excluded.name,
		elevation = excluded.elevation,
		latitude = excluded.latitude,
		longitude = excluded.longitude,
		category = excluded.category
`

// PassCategory classifies a pass for bike suitability: road = paved road,
// track = unpaved vehicle track, path = hiking trail, hiking = rock/climbing,
// unknown = not on a highway.
const (
	CategoryRoad    = "road"
	CategoryTrack   = "track"
	CategoryPath    = "path"
	CategoryHiking  = "hiking"
	CategoryUnknown = "unknown"
)

// ExtractMountainPasses scans pbfPath for mountain pass nodes and upserts them
// into the database. An optional reporter is invoked as scanning progresses
// with bytes scanned and the total file size, so callers (e.g. the CLI) can
// render progress. Category is derived from the highways of ways that contain
// the pass node (road > track > path) plus node tags (rock/climbing => hiking).
func ExtractMountainPasses(ctx context.Context, pbfPath string, db *sql.DB, reporters ...func(current, total int64)) (int, error) {
	info, err := os.Stat(pbfPath)
	if err != nil {
		return 0, fmt.Errorf("failed to stat pbf file: %w", err)
	}
	total := info.Size()
	report := func(int64, int64) {}
	if len(reporters) > 0 {
		report = reporters[0]
	}

	// Phase 1: collect pass nodes.
	type cachedPass struct {
		id        osm.NodeID
		name      string
		elevation any
		lat, lon  float64
		tags      osm.Tags
	}
	file, err := os.Open(pbfPath)
	if err != nil {
		return 0, fmt.Errorf("failed to open pbf file: %w", err)
	}
	reader := &countingReader{r: file}
	scanner := osmpbf.New(ctx, reader, 4)
	scanner.SkipWays = true
	scanner.SkipRelations = true
	scanner.FilterNode = isMountainPass

	cached := make([]cachedPass, 0, 4096)
	passSet := make(map[osm.NodeID]int, 4096) // node ID -> index in cached
	for scanner.Scan() {
		report(reader.n, total)
		node, ok := scanner.Object().(*osm.Node)
		if !ok {
			continue
		}
		elevation, hasElevation := parseElevation(node.Tags.Find("ele"))
		var elevationValue any
		if hasElevation {
			elevationValue = elevation
		}
		idx := len(cached)
		cached = append(cached, cachedPass{
			id:        node.ID,
			name:      node.Tags.Find("name"),
			elevation: elevationValue,
			lat:       float64(node.Lat),
			lon:       float64(node.Lon),
			tags:      node.Tags,
		})
		passSet[node.ID] = idx
	}
	if err := scanner.Err(); err != nil && err != io.EOF {
		file.Close()
		return 0, fmt.Errorf("failed to scan pbf nodes: %w", err)
	}
	file.Close()

	// Phase 2: scan ways to collect highways per pass.
	highwaysByPass := make(map[osm.NodeID][]string, len(cached))
	file2, err := os.Open(pbfPath)
	if err != nil {
		return 0, fmt.Errorf("failed to reopen pbf for ways: %w", err)
	}
	defer file2.Close()
	reader2 := &countingReader{r: file2}
	scanner2 := osmpbf.New(ctx, reader2, 4)
	scanner2.SkipNodes = true
	scanner2.SkipRelations = true
	for scanner2.Scan() {
		// Report second phase as second half of total for progress continuity.
		// We offset by total to avoid going backwards; callers use ratio anyway.
		report(reader2.n, total)
		way, ok := scanner2.Object().(*osm.Way)
		if !ok {
			continue
		}
		highway := way.Tags.Find("highway")
		// Keep even empty highway to detect non-highway ways? Only track highways.
		// We store only ways that actually represent a highway for categorisation;
		// non-highway ways are ignored (they keep pass as unknown).
		if highway == "" {
			continue
		}
		for _, nid := range way.Nodes {
			if _, ok := passSet[nid.ID]; ok {
				highwaysByPass[nid.ID] = append(highwaysByPass[nid.ID], highway)
			}
		}
	}
	if err := scanner2.Err(); err != nil && err != io.EOF {
		return 0, fmt.Errorf("failed to scan pbf ways: %w", err)
	}

	tx, err := db.BeginTx(ctx, nil)
	if err != nil {
		return 0, fmt.Errorf("failed to begin transaction: %w", err)
	}
	defer tx.Rollback()

	stmt, err := tx.PrepareContext(ctx, insertStatement)
	if err != nil {
		return 0, fmt.Errorf("failed to prepare insert: %w", err)
	}
	defer stmt.Close()

	count := 0
	for _, p := range cached {
		highways := highwaysByPass[p.id]
		category := categorizePass(p.tags, highways)
		if _, err := stmt.ExecContext(ctx, p.id, p.name, p.elevation, p.lat, p.lon, category); err != nil {
			return count, fmt.Errorf("failed to insert osm pass %d: %w", p.id, err)
		}
		count++
	}
	if err := tx.Commit(); err != nil {
		return count, fmt.Errorf("failed to commit transaction: %w", err)
	}
	slog.Info("Extracted mountain passes", "count", count, "source", pbfPath)
	return count, nil
}

func categorizePass(tags osm.Tags, highways []string) string {
	natural := tags.Find("natural")
	sport := tags.Find("sport")
	isHikingNode := natural == "rock" || sport == "climbing"
	for _, h := range highways {
		if isRoadHighway(h) {
			return CategoryRoad
		}
	}
	if isHikingNode {
		return CategoryHiking
	}
	for _, h := range highways {
		if h == "track" {
			return CategoryTrack
		}
	}
	for _, h := range highways {
		if isPathHighway(h) {
			return CategoryPath
		}
	}
	return CategoryUnknown
}

func isRoadHighway(highway string) bool {
	switch highway {
	case "motorway", "motorway_link", "trunk", "trunk_link", "primary", "primary_link", "secondary", "secondary_link", "tertiary", "tertiary_link", "unclassified", "residential", "service", "living_street", "road", "pedestrian":
		return true
	default:
		return false
	}
}

func isPathHighway(highway string) bool {
	switch highway {
	case "path", "footway", "cycleway", "bridleway", "steps", "via_ferrata":
		return true
	default:
		return false
	}
}

// countingReader tracks the number of bytes read from an underlying reader,
// used to report scan progress against the PBF file size.
type countingReader struct {
	r io.Reader
	n int64
}

func (c *countingReader) Read(p []byte) (int, error) {
	n, err := c.r.Read(p)
	c.n += int64(n)
	return n, err
}

func isMountainPass(node *osm.Node) bool {
	if node.Tags.Find("mountain_pass") == "yes" {
		return true
	}
	return node.Tags.Find("natural") == "mountain_pass"
}

func parseElevation(ele string) (int, bool) {
	ele = strings.TrimSpace(ele)
	if ele == "" {
		return 0, false
	}
	for candidate := range strings.FieldsSeq(ele) {
		if value, err := strconv.Atoi(candidate); err == nil {
			return value, true
		}
		if value, err := strconv.ParseFloat(candidate, 64); err == nil {
			return int(value), true
		}
	}
	return 0, false
}