From 49cb2774e23f4e58b6cb56fa093ad984660eecf7 Mon Sep 17 00:00:00 2001
From: Philipp Wolfer <ph.wolfer@gmail.com>
Date: Fri, 10 Nov 2023 00:56:43 +0100
Subject: [PATCH] listenbrainz: Read data from newest first

Very low min_ts parameters lead to empty results from LB and there is no
easy way to determine the oldest valid timestamp.
---
 backends/listenbrainz.go        | 24 ++++++++++++++++--------
 backends/listenbrainz/client.go |  5 +++--
 2 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/backends/listenbrainz.go b/backends/listenbrainz.go
index 0ef6127..84fee97 100644
--- a/backends/listenbrainz.go
+++ b/backends/listenbrainz.go
@@ -22,6 +22,7 @@ THE SOFTWARE.
 package backends
 
 import (
+	"slices"
 	"time"
 
 	"github.com/spf13/viper"
@@ -41,11 +42,13 @@ func (b ListenBrainzApiBackend) FromConfig(config *viper.Viper) Backend {
 }
 
 func (b ListenBrainzApiBackend) ExportListens(oldestTimestamp time.Time) ([]Listen, error) {
-	minTs := oldestTimestamp
+	maxTime := time.Now()
+	minTime := time.Unix(0, 0)
 	listens := make([]Listen, 0)
 
+out:
 	for {
-		result, err := b.client.GetListens(b.username, minTs)
+		result, err := b.client.GetListens(b.username, maxTime, minTime)
 		if err != nil {
 			return nil, err
 		}
@@ -55,16 +58,21 @@ func (b ListenBrainzApiBackend) ExportListens(oldestTimestamp time.Time) ([]List
 			break
 		}
 
-		// Set minTs to the newest returned listen
-		minTs = time.Unix(result.Payload.Listens[0].ListenedAt, 0)
+		// Set maxTime to the oldest returned listen
+		maxTime = time.Unix(result.Payload.Listens[count-1].ListenedAt, 0)
 
-		// Iterate over the returned listens in reverse order (oldest first)
-		for i := count - 1; i >= 0; i-- {
-			lbListen := result.Payload.Listens[i]
-			listens = append(listens, Listen{}.FromListenBrainz(lbListen))
+		for _, listen := range result.Payload.Listens {
+			if listen.ListenedAt > oldestTimestamp.Unix() {
+				listens = append(listens, Listen{}.FromListenBrainz(listen))
+			} else {
+				// result contains listens older then oldestTimestamp,
+				// we can stop requesting more
+				break out
+			}
 		}
 	}
 
+	slices.Reverse(listens)
 	return listens, nil
 }
 
diff --git a/backends/listenbrainz/client.go b/backends/listenbrainz/client.go
index ded8ce4..b458649 100644
--- a/backends/listenbrainz/client.go
+++ b/backends/listenbrainz/client.go
@@ -52,13 +52,14 @@ func New(token string) Client {
 	return client
 }
 
-func (c Client) GetListens(user string, minTs time.Time) (GetListensResult, error) {
+func (c Client) GetListens(user string, maxTime time.Time, minTime time.Time) (GetListensResult, error) {
 	const path = "/user/{username}/listens"
 	result := &GetListensResult{}
 	_, err := c.resty.R().
 		SetPathParam("username", user).
 		SetQueryParams(map[string]string{
-			"min_ts": strconv.FormatInt(minTs.Unix(), 10),
+			"max_ts": strconv.FormatInt(maxTime.Unix(), 10),
+			"min_ts": strconv.FormatInt(minTime.Unix(), 10),
 			"count":  strconv.FormatInt(int64(c.MaxResults), 10),
 		}).
 		SetResult(result).