package gateway

import (
	"context"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/textproto"
	"strconv"
	"strings"

	mc "github.com/multiformats/go-multicodec"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/trace"
)

func (i *handler) serveDefaults(ctx context.Context, w http.ResponseWriter, r *http.Request, rq *requestData) bool {
	ctx, span := spanTrace(ctx, "Handler.ServeDefaults", trace.WithAttributes(attribute.String("path", rq.contentPath.String())))
	defer span.End()

	var (
		pathMetadata ContentPathMetadata
		err          error
		ranges       []ByteRange
		headResp     *HeadResponse
		getResp      *GetResponse
	)

	switch r.Method {
	case http.MethodHead:
		pathMetadata, headResp, err = i.backend.Head(ctx, rq.mostlyResolvedPath())
		if err != nil {
			if isWebRequest(rq.responseFormat) {
				forwardedPath, continueProcessing := i.handleWebRequestErrors(w, r, rq.mostlyResolvedPath(), rq.immutablePath, rq.contentPath, err, rq.logger)
				if !continueProcessing {
					return false
				}
				pathMetadata, headResp, err = i.backend.Head(ctx, forwardedPath)
				if err != nil {
					err = fmt.Errorf("failed to resolve %s: %w", debugStr(rq.contentPath.String()), err)
					i.webError(w, r, err, http.StatusInternalServerError)
					return false
				}
			} else {
				if !i.handleRequestErrors(w, r, rq.contentPath, err) {
					return false
				}
			}
		}
		defer headResp.Close()
	case http.MethodGet:
		rangeHeader := r.Header.Get("Range")
		if rangeHeader != "" {
			// Note: proper tests for Range parsing live in https://github.com/ipfs/gateway-conformance
			ranges, err = parseRangeWithoutLength(rangeHeader)
			if err != nil {
				i.webError(w, r, fmt.Errorf("invalid range request: %w", err), http.StatusBadRequest)
				return false
			}
		}

		// TODO: passing only resolved path here, instead of contentPath is
		// harming content routing. Knowing original immutableContentPath will
		// allow backend to find providers for parents, even when internal
		// CIDs are not announced, and will provide better key for caching
		// related DAGs.
		pathMetadata, getResp, err = i.backend.Get(ctx, rq.mostlyResolvedPath(), ranges...)
		if err != nil {
			if isWebRequest(rq.responseFormat) {
				forwardedPath, continueProcessing := i.handleWebRequestErrors(w, r, rq.mostlyResolvedPath(), rq.immutablePath, rq.contentPath, err, rq.logger)
				if !continueProcessing {
					return false
				}
				pathMetadata, getResp, err = i.backend.Get(ctx, forwardedPath, ranges...)
				if err != nil {
					err = fmt.Errorf("failed to resolve %s: %w", debugStr(rq.contentPath.String()), err)
					i.webError(w, r, err, http.StatusInternalServerError)
					return false
				}
			} else {
				if !i.handleRequestErrors(w, r, rq.contentPath, err) {
					return false
				}
			}
		}
		defer getResp.Close()
	default:
		// This shouldn't be possible to reach which is why it is a 500 rather than 4XX error
		i.webError(w, r, errors.New("invalid method: cannot use this HTTP method with the given request"), http.StatusInternalServerError)
		return false
	}

	setIpfsRootsHeader(w, rq, &pathMetadata)

	// On deserialized responses, we prefer Last-Modified from pathMetadata
	// (mtime in UnixFS 1.5 DAG). This also applies to /ipns/, because value
	// from dag-pb, if present, is more meaningful than lastMod inferred from
	// namesys.
	if !pathMetadata.ModTime.IsZero() {
		rq.lastMod = pathMetadata.ModTime
	}

	resolvedPath := pathMetadata.LastSegment
	switch mc.Code(resolvedPath.RootCid().Prefix().Codec) {
	case mc.Json, mc.DagJson, mc.Cbor, mc.DagCbor:
		rq.logger.Debugw("serving codec", "path", rq.contentPath)
		var blockSize int64
		var dataToRender io.ReadSeekCloser
		if headResp != nil {
			blockSize = headResp.bytesSize
			dataToRender = nil
		} else {
			blockSize = getResp.bytesSize
			dataAsReadSeekCloser, ok := getResp.bytes.(io.ReadSeekCloser)
			if !ok {
				i.webError(w, r, errors.New("expected returned non-UnixFS data to be seekable"), http.StatusInternalServerError)
			}
			dataToRender = dataAsReadSeekCloser
		}

		return i.renderCodec(r.Context(), w, r, rq, blockSize, dataToRender)
	default:
		rq.logger.Debugw("serving unixfs", "path", rq.contentPath)
		ctx, span := spanTrace(ctx, "Handler.ServeUnixFS", trace.WithAttributes(attribute.String("path", resolvedPath.String())))
		defer span.End()

		// Handle UnixFS HEAD requests
		if headResp != nil {
			if headResp.isFile {
				rq.logger.Debugw("serving unixfs file", "path", rq.contentPath)
				return i.serveFile(ctx, w, r, resolvedPath, rq, headResp.bytesSize, headResp.startingBytes, false, true, pathMetadata.ContentType)
			} else if headResp.isSymLink {
				rq.logger.Debugw("serving unixfs file", "path", rq.contentPath)
				return i.serveFile(ctx, w, r, resolvedPath, rq, headResp.bytesSize, nil, true, true, pathMetadata.ContentType)
			} else if headResp.isDir {
				rq.logger.Debugw("serving unixfs directory", "path", rq.contentPath)
				return i.serveDirectory(ctx, w, r, resolvedPath, rq, true, nil, ranges)
			}
		} else {
			if getResp.bytes != nil {
				rq.logger.Debugw("serving unixfs file", "path", rq.contentPath)
				rangeRequestStartsAtZero := true
				if len(ranges) > 0 {
					ra := ranges[0]
					if ra.From != 0 {
						rangeRequestStartsAtZero = false
					}
				}
				return i.serveFile(ctx, w, r, resolvedPath, rq, getResp.bytesSize, getResp.bytes, false, rangeRequestStartsAtZero, pathMetadata.ContentType)
			} else if getResp.symlink != nil {
				rq.logger.Debugw("serving unixfs file", "path", rq.contentPath)
				// Note: this ignores range requests against symlinks
				return i.serveFile(ctx, w, r, resolvedPath, rq, getResp.bytesSize, getResp.symlink, true, true, pathMetadata.ContentType)
			} else if getResp.directoryMetadata != nil {
				rq.logger.Debugw("serving unixfs directory", "path", rq.contentPath)
				return i.serveDirectory(ctx, w, r, resolvedPath, rq, false, getResp.directoryMetadata, ranges)
			}
		}

		i.webError(w, r, errors.New("unsupported UnixFS type"), http.StatusInternalServerError)
		return false
	}
}

// parseRangeWithoutLength parses a Range header string as per RFC 7233.
func parseRangeWithoutLength(s string) ([]ByteRange, error) {
	if s == "" {
		return nil, nil // header not present
	}
	const b = "bytes="
	if !strings.HasPrefix(s, b) {
		return nil, errors.New("invalid range")
	}
	var ranges []ByteRange
	for _, ra := range strings.Split(s[len(b):], ",") {
		ra = textproto.TrimString(ra)
		if ra == "" {
			continue
		}
		start, end, ok := strings.Cut(ra, "-")
		if !ok {
			return nil, errors.New("invalid range")
		}
		start, end = textproto.TrimString(start), textproto.TrimString(end)
		var r ByteRange
		if start == "" {
			r.To = nil
			// If no start is specified, end specifies the
			// range start relative to the end of the file,
			// and we are dealing with <suffix-length>
			// which has to be a non-negative integer as per
			// RFC 7233 Section 2.1 "Byte-Ranges".
			if end == "" || end[0] == '-' {
				return nil, errors.New("invalid range")
			}
			i, err := strconv.ParseInt(end, 10, 64)
			if i < 0 || err != nil {
				return nil, errors.New("invalid range")
			}
			r.From = -i
		} else {
			i, err := strconv.ParseInt(start, 10, 64)
			if err != nil {
				return nil, errors.New("invalid range")
			}
			r.From = i
			if end == "" {
				// If no end is specified, range extends to end of the file.
				r.To = nil
			} else {
				i, err := strconv.ParseInt(end, 10, 64)
				if err != nil || i < 0 || r.From > i {
					return nil, errors.New("invalid range")
				}
				r.To = &i
			}
		}
		ranges = append(ranges, r)
	}
	return ranges, nil
}
